Developing a simple, low cost CO2 sensor is a goal that continues to be attempted with limited success. Carbon dioxide is very stable and hard to catalyze into ionic groups which could then be used for simple conductometric detection. Current methods for CO2 detection consist of:
(i) non-dispersive infrared (NDIR) sensors having an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measures the absorption of the characteristic wavelength of light (Advantages—Sensitivities of 20-50 PPM, selective to error less than 10% solid state giving a life-time up to 10 years; Disadvantages—Very costly, typical NDIR sensors are still in the $100-$1000 range, relatively large and bulky);
(ii) Chemical CO2 gas sensors with sensitive layers based on polymer, polymer arrays, metal oxides and new nanomaterials such as nanotubes and nanowires have the principal advantage of very low energy consumption and can be reduced in size to fit into microelectronic-base systems. On the downside, short- and long term drift effects as well as a rather low overall lifetime are major obstacles when compared with the NDIR measurement principle; and (iii) other methods include optical fiber based sensors and MEMS based sensors.